U.S. patent number 6,942,820 [Application Number 10/832,265] was granted by the patent office on 2005-09-13 for dimethylpolysiloxane composition.
This patent grant is currently assigned to Shin-Etsu Chemical Co., Ltd.. Invention is credited to Toshiaki Ihara, Masahiko Minemura, Hiroshi Nakayama, Ichiro Ono, Sinobu Sato.
United States Patent |
6,942,820 |
Ihara , et al. |
September 13, 2005 |
Dimethylpolysiloxane composition
Abstract
A dimethylpolysiloxane composition comprising at least two
dimethylpolysiloxanes selected from dimethylpolysiloxanes
represented by formula (1) or formula (2), ##STR1## wherein m is an
integer with 0.ltoreq.m.ltoreq.10 and n is an integer with
3.ltoreq.n.ltoreq.10, one of said at least two
dimethylpolysiloxanes is dodecamethylpentasiloxane contained in an
amount of 15 to 95 wt % based on a total weight of the composition,
and the composition has a moisture content of at most 50 ppm based
on the total weight of the composition.
Inventors: |
Ihara; Toshiaki (Gunma,
JP), Sato; Sinobu (Annaka, JP), Ono;
Ichiro (Gunma, JP), Nakayama; Hiroshi (Annaka,
JP), Minemura; Masahiko (Gunma, JP) |
Assignee: |
Shin-Etsu Chemical Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
32993099 |
Appl.
No.: |
10/832,265 |
Filed: |
April 27, 2004 |
Foreign Application Priority Data
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Apr 28, 2003 [JP] |
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2003-123355 |
Apr 13, 2004 [JP] |
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2004-118319 |
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Current U.S.
Class: |
252/69; 252/67;
252/78.3 |
Current CPC
Class: |
C08L
83/04 (20130101); C09K 5/10 (20130101); C08L
83/04 (20130101); C08L 83/00 (20130101) |
Current International
Class: |
C09K
5/10 (20060101); C09K 5/00 (20060101); C09K
005/10 () |
Field of
Search: |
;252/67,69,78.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2001-262168 |
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Sep 2001 |
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JP |
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1004410 |
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Mar 1983 |
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RU |
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Primary Examiner: Moore; Margaret G.
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Claims
What is claimed is:
1. A dimethylpolysiloxane composition comprising at least two
dimethylpolysiloxanes selected from dimethylpolysiloxanes
represented by formula (1) or formula (2), ##STR4##
wherein m is an integer with 0.ltoreq.m.ltoreq.10 and n is an
integer with 3.ltoreq.n.ltoreq.10, one of said at least two
dimethylpolysiloxanes is dodecamethylpentasiloxane contained in an
amount of 15 to 95 wt % based on a total weight of the composition,
and the composition has a moisture content of at most 50 ppm based
on the total weight of the composition, a viscosity of 2 mm.sup.2
/s or smaller at 25 degrees C. and a viscosity of 300 mm.sup.2 /s
or smaller at -100 degrees C.
2. The dimethylpolysiloxane composition according to claim 1,
wherein the composition has a freezing point of -110 degrees C. or
lower.
3. The dimethylpolysiloxane composition according to claim 1 or 2,
wherein the composition comprises at least 1 wt %, based on the
total weight of the composition, of the cyclic dimethylpolysiloxane
represented by the formula (2).
4. A refrigerant for an apparatus comprising the composition
according to claim 1 or 2.
Description
CROSS REFERENCE
This application claims benefits of Japanese Patent application No.
2003-123355 filed on Apr. 28, 2003, and Japanese Patent application
No. 2004-118319 filed on Apr. 13, 2004, the contents of which are
hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a composition which can be used as
a refrigerant and does not freeze, and is fluid with a low
viscosity even at a temperature so low as -100 degrees C. The
composition is safe and can be produced at low cost.
DESCRIPTION OF THE PRIOR ART
A silicone oil is used as a refrigerant for various industrial
apparatuses because it is physiologically and ecologically highly
safe; it has a relatively low pour point and a freezing point; and
it shows a small increase in viscosity with decreasing temperature.
Especially, a linear dimethylpolysiloxane having a viscosity of
from 1 to 10 mm.sup.2 /s at 25 degrees C. is widely used as a
refrigerant.
Pour point and freezing point data of a dimethylpolysiloxane having
a low viscosity and good low-temperature properties are varied
among silicone producers as can be seen between the technical
information sheet, "Performance data of silicone oil KF96",
Shin-Etsu Chemical Co., Ltd, and the product catalogue, "200 Fluid
Typical Properties", Dow Corning Co. Reasons for this variance may
be difficulty in measurements of pour point and freezing point at a
very low temperature, and influence of moisture remaining in the
dimethylpolysiloxane on pour point and freezing point. At present,
the lowest applicable temperature of a dimethylpolysiloxane as an
industrial refrigerant is not lower than a temperature of from -80
to -90 degrees C.
SUMMARY OF THE INVENTION
Recently, there arise needs for an industrial refrigerant which
does not freeze to have steady fluidity even at a temperature of
-100 degrees C. or lower. The present inventors dehydrated various
dimethylpolysiloxanes having low viscosity and precisely measured
their pour points and freezing points. It has been found that
dodecamethylpentasiloxane has the best low-temperature properties
against the data so far reported.
However, dodecamethylpentasiloxane has drawbacks. One drawback is
high production cost. Dodecamethylpentasiloxane is produced by the
following process:
1) mixing a mixture of cyclic siloxanes produced by subjecting
dimethyldichlorosilane to hydrolysis and condensation reaction, and
a siloxane of the formula, (CH.sub.3).sub.3 SiOSi(CH.sub.3).sub.3,
produced by subjecting trimethyldichlorosilane to a hydrolysis and
condensation reaction in a predetermined ratio,
2) subjecting the mixture obtained in the step 1) to a
redistribution reaction in the presence of an acid catalyst such as
sulfuric acid and a solid acid catalyst to produce a mixture of
various siloxanes, and
3) isolating dodecamethylpentasiloxane from the mixture of various
siloxanes by a fractional distillation.
The high production cost is due to low production per hour in the
fractional distillation process of step 3).
Another drawback is that dodecamethylpentasiloxane has a viscosity
of 2 mm.sup.2 /s at 25 degrees C. For an industrial refrigerant
application, a dimethylpolysiloxane having a viscosity lower than 2
mm.sup.2 /s is preferred because such dimethylpolysiloxane has
higher thermal conductivity, higher fluidity, and lower friction
torque.
Therefore, a refrigerant is desired which has as good
low-temperature properties as dodecamethylpentasiloxane, but has a
lower viscosity and lower production cost than
dodecamethylpentasiloxane.
The present inventors have found that dodecamethylpentasiloxane has
an interesting property that it does not show any melting peak in
scanning differential calorimetry (DSC). This may be because
dodecamethylpentasiloxane has a three-dimensional structure
difficult to form a crystal. It has also been found that a mixture
of dodecamethylpentasiloxane with an other dimethylpolysiloxane
does not show any melting peak as far as the mixture contains at
least 15 wt % of dodecamethylpentasiloxane based on a total weight
of the mixture.
In addition, it has been found with surprise that such a mixture
has a freezing point and a pour point both lower than -100 degrees
C. Further, such a mixture containing at least 5 wt % of the other
dimethylpolysiloxanes having a viscosity lower than 2 mm.sup.2 /s
at 25 degrees C. was found to have a viscosity lower than 2
mm.sup.2 /s at 25 degrees C., as well as a freezing point and a
pour point lower than -100 degrees C.
Thus, the present invention is a dimethylpolysiloxane composition
comprising at least two dimethylpolysiloxanes selected from
dimethylpolysiloxanes represented by formula (1) or formula (2),
##STR2##
wherein m is an integer with 0.ltoreq.m.ltoreq.10 and n is an
integer with 3.ltoreq.n.ltoreq.10,
one of said at least two dimethylpolysiloxanes is
dodecamethylpentasiloxane contained in an amount of 15 to 95 wt %
based on a total weight of the composition, and the composition has
a moisture content of at most 50 ppm based on the total weight of
the composition.
Preferred embodiments of the above invention are as follows.
The dimethylpolysiloxane composition described above, wherein the
composition has a viscosity of 2 mm.sup.2 /s or smaller at 25
degrees C. and a viscosity of 300 mm.sup.2 /s or smaller at -100
degrees C.
The dimethylpolysiloxane composition described above, wherein the
composition has a freezing point of -110 degrees C. or lower.
The composition described above, wherein the composition comprises
at least 1 wt %, based on the total weight of the composition, of
the cyclic dimethylpolysiloxane represented by the formula (2).
The present invention relates also to a refrigerant for an
apparatus comprising the composition described above.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is a dimethylpolysiloxane composition
comprising at least two dimethylpolysiloxanes selected from
dimethylpolysiloxanes represented by formula (1) or formula (2). In
the formulae, m is an integer with 0.ltoreq.m.ltoreq.10, preferably
0.ltoreq.m.ltoreq.6, and n is an integer with 3.ltoreq.n.ltoreq.10,
preferably 4.ltoreq.n.ltoreq.8. Examples of the
dimethylpolysiloxane include linear siloxanes such as
hexamethyldisiloxane, octametyltrisiloxane,
decamethyltetrasiloxane, dodecamethylpentasiloxane,
tetradecamethylhexasiloxane, hexadecamethylheptasiloxane,
octadecamethyloctasiloxane, and eicosarmethylnonasiloxane; cyclic
siloxanes such as hexamethylcyclotrisiloxane,
octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,
dodecamethylcyclohexasiloxane, and
tetradecamethylcycloheptasiloxane.
In the aforesaid production process of dodecamethylpentasiloxane,
dimethyldichlorosilane is subjected to hydrolysis and a
condensation reaction to obtain a mixture of cyclic siloxanes of
the formula (2). A reaction product of a redistribution reaction of
the mixture of cyclic siloxanes with (CH.sub.3).sub.3 SiOSi
(CH.sub.3)3 is a mixture of the siloxanes or the formulae (1) and
(2). Next, in isolating dodecamethylpentasiloxane from the mixture,
separation of dodecamethylpentasiloxane from octamethyltrisiloxane
and decamethyltetrasiloxane takes long time because the boiling
points of octamethyltrisiloxane and decamethyltetrasiloxane are
close to that of dodecamethylpentasiloxane. This results in a low
production rate and high production cost.
The present composition is characterized in that
dimethylpolysiloxanes other than dodecamethylpentasiloxane are
contained in such an amount that the low-temperature properties of
dodecamethylpentasiloxane are not adversely affected. This is based
on the present inventors' finding that dodecamethylpentasiloxane
has a peculiar property of showing no melting peak in DSC and its
low-temperature properties are maintained in a mixture with other
dimethylpolysiloxanes in a certain amount. Such other
dimethylpolysiloxanes include other fractions obtained in simple
distillations and dimethylpolysiloxanes distilled off together with
dodecamethylpentasiloxane under weaker distillation conditions than
precision fractional distillation of dodecamethylpentasiloxane. On
account of these dimethylpolysiloxanes, the present composition can
be obtained at a significantly lower cost than that of
dodecamethylpentasiloxane, and makes use of the good
low-temperature properties of dodecamethylpentasiloxane.
In the composition, dodecamethylpentasiloxane is contained in an
amount of from 15 to 95 wt %, preferably from 20 to 70 wt %, based
on a total weight of the composition. If the amount is below the
aforesaid lower limit, a composition may freeze or have a viscosity
larger than 300 mm.sup.2 /s at -100 degrees C. If the amount
exceeds the aforesaid upper limit, a production rate in
distillation process is lower, leading to higher production
cost.
Among the aforesaid dimethylpolysiloxanes described above,
preferred dimethylpolysiloxanes other than
dodecamethylpentasiloxane include hexamethyldisiloxane,
octamethyltrisiloxane, decamethyltetrasiloxane,
tetradecamethylhexasiloxane, octamethylcyclotetrasiloxane,
decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane,
because of their low viscosity and good flow property.
Preferably, the composition comprises at least 1 wt %, more
preferably at least 5 wt %, of the cyclic dimethylpolysiloxane of
the formula (2) in the viewpoint of production cost.
The present composition has a moisture content of at most 50 ppm,
preferably at most 30 ppm. A moisture content larger than 50 ppm
causes a pour point to rise, so that a composition may not attain
the aimed flow property and viscosity at a temperature below -100
degrees C. without freezing. The moisture can be removed by any
known method such as purging moisture by blowing dry nitrogen gas
into the composition.
The present dimetylpolysiloxane composition has a viscosity at 25
degrees C. of 2 mm.sup.2 /s or smaller, preferably 1.7 mm.sup.2 /s
or smaller, and a viscosity at -100 degrees C. of 300 mm.sup.2 /S
or smaller, preferably 100 mm.sup.2 /s or smaller. A composition
having a viscosity at 25 degrees C. of higher than 2 mm.sup.2 /s is
undesirable because such a composition highly likely has a
viscosity at -100 degrees C greater than 300 mm.sup.2 S. A
composition having a viscosity at 25 degrees C. of 2 mm.sup.2 /s or
smaller, but having a viscosity at -100 degrees C. greater than 300
mm.sup.2 /S is undesirable, because such a composition may show
drastic change in properties, such as thermal conductivity,
specific heat, flow property and friction torque, at different
temperature.
Industrial apparatuses in which the present composition can be
suitably used include pharmaceuticals production units, freezers
used in the agricultural, stock raising or fishery industry, ice
making and freezing warehouses, super low temperature
refrigerators, adsorption refrigerators in atomic power plants,
freezers for storing frozen foods or processed marine products,
freezers in freezing carriers, helium liquefiers, cooling systems
of helical superconducting magnets, cryoprobes, i.e., clinical
cryogenic spot cooling machine, cryosurgery apparatuses for cancer
treatment, cooling systems of superconducting magnets to float a
linear motor train, cooling systems of hydrogen fuel liquefiers of
space rockets, and vacuum freeze-driers used in the drug or food
industry, but are not limited to these.
EXAMPLES
The present invention will be explained with reference to the
following non-limiting Examples and Comparative Examples, but not
limited thereto. The amounts are represented in wt % unless
otherwise specified.
The properties of the dimethylpolysiloxanes shown in Table 1 were
measured after dehydrating each dimethylpolysiloxane to a moisture
content to the value specified in Table 1.
The following dimethylpolysiloxanes were used.
M.sub.2 : KF-96 having a viscosity of 0.65 mm.sup.2 /s, ex
Shin-Etsu Chemical Co., Ltd.
M.sub.2 D: KF-96 having a viscosity of 1 mm.sup.2 /s, ex Shin-Etsu
Chemical Co., Ltd.
M.sub.2 D.sub.2 : KF-96 having a viscosity of 1.5 mm.sup.2 /S, ex
Shin-Etsu Chemical Co., Ltd.
M.sub.2 D.sub.3 : KF-96 having a viscosity of 2 mm.sup.2 /s, ex
Shin-Etsu Chemical Co. Ltd.
M.sub.2 D.sub.4, M.sub.2 D.sub.5, M.sub.2 D.sub.6 : prepared from a
mixture of KF-96 having a viscosity of 2 mm.sup.2 /s and KF-96
having a viscosity of 2 mm.sup.2 /s, ex Shin-Etsu Chemical Co.,
Ltd.
D4: KF-994, ex Shin-Etau Chemical Co., Ltd.
D5: KF-995, ex Shin-Etsu Chemical Co., Ltd.
The symbols "M", "D", D4 and D5, represent the following chemical
structures. ##STR3##
The properties were determined according to the following
methods.
Pour Point
A pour point was measured according to the Japanese Industrial
Standards, JIS-K-2269. A composition was cooled in a cooling bath
containing liquid nitrogen. A moisture content of each composition
was adjusted by blowing nitrogen gas via a glass pipette in 45 g of
the composition for 30 minutes. The moisture content of the
composition was measured with a Karl-fisher moisture meter.
Freezing Point
A freezing point was measured according to JIS-K-0065. A bath
containing liquid nitrogen was used. A moisture content of each
composition was adjusted in the same manner as described above.
Viscosity
A viscosity at 25 degrees C or at -100 degrees C. was measured
according to JIS-Z-8803. A compositions was cooled in a cooling
bath containing liquid nitrogen to measure the viscosity at -100
degrees C. In Table 1, the abbreviation, "NG", means that the
viscosity at -100 degrees C. could not be measured.
TABLE 1 Properties of the dimethylpolysiloxanes viscosity viscosity
freezing moisture dimethyl- (25.degree. C. (-100.degree. C. pour
point point content polysiloxane mm.sup.2 /s) mm.sup.2 /s)
(.degree. C.) (.degree. C.) (ppm) M.sub.2 D.sub.3 * 2.0 100 -120
-120 20 M.sub.2 D.sub.3 ** 2.0 336 -107 -107 50 M.sub.2 D.sub.3 ***
2.0 NG -86 -87 200 M.sub.2 0.65 NG -77 -70 20 M.sub.2 D 1.0 NG -100
-90 20 M.sub.2 D.sub.2 1.5 NG -95 -95 20 M.sub.2 D.sub.4 2.6 NG -90
-88 20 M.sub.2 D.sub.5 3.2 NG -70 -70 20 M.sub.2 D.sub.6 3.9 NG -67
-67 20 D4 2.3 NG 17 18 20 D5 3.9 NG -40 -40 20 D6 6.6 NG -85 -85
20
As shown in Table 1, the pour point and the freezing point rise
with the increasing moisture content.
Example 1
A reaction product obtained by subjecting trimethylchlorosilane to
a hydrolysis and condensation reaction and a reaction product
obtained by subjecting dimethyldichlorosilane to a hydrolysis and
condensation reaction were mixed at a molar ratio of 2:3. The
mixture was then placed in a 5 m.sup.3 SUS reactor and subjected to
a redistribution reaction in the presence of a solid catalyst, a
sulfonated styrene/divinylbenzene copolymer, at a constant
temperature of 70 degrees C. The reaction product obtained was
subjected to a simple distillation at a temperature of 105 degrees
C. and a pressure of 2700 Pa. The bottom product of the
distillation was then subjected to a simple distillation at a
temperature of 105 degrees C. and a pressure of 400 Pa to obtain a
composition of Example 1. The composition was analyzed by capillary
gas chromatography with a capillary column, DB-1701, a temperature
increase rate of 15 degrees C./min from 50 degrees C. to 300
degrees C.
Example 2
The composition of Example 2 was prepared in the same manner as in
Example 1 except that the second simple distillation was carried
out at a pressure of 270 Pa. The composition obtained was analyzed
in the same method as in Example 1.
Examples 3, 4 and Comparative Example 5
Compositions of Examples 3, 4 and Comparative Example 5 were
prepared by mixing dodecamethylpentasiloxane with
decamethyltetrasiloxane or octamethyltrisiloxane in a wt % as seen
in Table 2. The dodecamethylpentasiloxane, decamethyltetrasiloxane
and octamethyltrisiloxane had been isolated by distillation from
the redistribution reaction product described in Example 1.
The compositions and properties are as shown in Table 2.
TABLE 2 Properties of Dimethylpolysiloxane Compositions Exam- Exam-
Comparative Comparative Comparative Comparative Comparative
Comparative Example 1 Example 2 ple 3 ple 4 Example 1 Example 2
Example 3 Example 4 Example 5 Example 6 dimethyl- polysiloxane (wt
%) M.sub.2 D.sub.3 * 18 25 30 30 10 M.sub.2 D.sub.3 ** 100 M.sub.2
D.sub.3 *** 100 M.sub.2 2 1 100 M.sub.2 D 15 11 70 100 M.sub.2
D.sub.2 25 27 70 100 90 M.sub.2 D.sub.4 7 12 M.sub.2 D.sub.5 3 4
M.sub.2 D.sub.6 1 2 D4 17 10 D5 10 7 D6 2 1 Properties of
composition viscosity(25.degree. C., 1.9 2.0 1.65 1.3 0.65 1.0 1.5
2.0 1.55 2.0 mm.sup.2 /s) viscosity(-100.degree. C., 148 148 100 80
NG NG NG NG NG 336 mm.sup.2 /s) pour -118 -118 -114 -114 -77 -100
-95 -86 -91 -107 point (.degree. C.) freezing point -120 -120 -118
-116 -70 -90 -95 -87 -92 -107 (.degree. C.) moisture 20 20 20 20 20
20 20 200 20 50 content(ppm) production per A A B B B B B C B C
hour In the Table 2, the ratings, A, B, and C, of the production
per hour mean as follows: A: a production per hour 10 times or more
as much as that of dodecamethylpentasiloxane, B: a production per
hour 3 to 10 times as much as that of dodecamethylpentasiloxane, C:
a production per hour 1 to 3 times as much as that of
dodecamethylpentasiloxane.
In the table 2, the ratings, A, B, and C, of the production per
hour mean as follows:
A: a production per hour 10 times or more as much as that of
dodecamethylpentasiloxane,
B: a production per hour 3 to 10 times as much as that of
dodecamethylpentasiloxane,
C: a production per hour 1 to 3 times as much as that of
dodecamethylpentasiloxane.
As shown in Table 2, the present composition makes use of low
viscosity and high production of dimethylpolysiloxanes other than
dodecametylpentasiloxane, while taking advantage of the
low-temperature properties of dodecametylpentasiloxane. The present
composition is suitable for an industrial refrigerant.
* * * * *